The goal of this research is to discover how social interactions are translated into functional changes in the brain. I proposed experiments that will identify neural pathways by which social interactions among male teleosts control gonadotropin releasing hormone (GnRH-I) neurons. Becoming socially dominant produces an 8-fold increase in their size of GnRH-I neurons while social descent causes those same neurons to shrink. It is not known, however, how social information reaches the brain regions that control GnRH-I. The specific aims are: 1) To identify functional circuits responsible for social regulation of reproduction using expression of the immediate early genes (IEG), c- FOS and erg-1 in appropriate social situations. Specifically, I will compare IEG induction of males in social transitions to males in stable social situations, to discover the time-course of activation, including when GnRH-I neurons are, themselves, activated. 2) I will map projections from sensory and motivational systems to GnRH-I neurons of the pre-optic area using a transsynaptic tracer, fragment C of tetnus toxin. By combining functional and neuroanatomical analyses with manipulation of the animal's social status, these experiments will add significantly to our understanding of how social information influences the brain. Regulation of reproduction by GnRH-I is highly conserved among vertebrates so that understanding the mechanisms by which social cues influence GnRH-I neurons is essential to a better understanding of numerous reproductive pathologies.